Question

Toughness index gives a measure of shear strength of soil at _____.

• A. Plastic limit
• B. Liquid limit
• C. Shrinkage limit
• D. Dry state

Hint:

Remember: \[ \boxed{ I_t=\frac{I_p}{I_f} } \] Toughness index indicates the soil's shear strength near the plastic limit.

Answer 1

The Correct Option is A

Concept: The toughness index (\(I_t\)) is defined as \[ \boxed{ I_t=\frac{I_p}{I_f} } \] where \[ I_p=\text{Plasticity Index}, \] \[ I_f=\text{Flow Index}. \] It indicates the toughness and shear strength characteristics of soil near its plastic limit.

Step 1: Understand the significance of toughness index. A higher toughness index indicates greater resistance to deformation and higher shear strength at the plastic limit.

Step 2: Identify the correct moisture condition. Hence, \[ \boxed{\text{Toughness index measures the shear strength of soil at the plastic limit}.} \] Therefore, the correct option is \[ \boxed{(A)\;\text{Plastic limit}.} \]